In oil and gas exploration, hydrocarbons or the customary hydrocarbon-water mixtures are often found in unconsolidated sand and rock layers. Production can discharge sand particles from the rock formation together with the hydrocarbon-water mixture as a result of the shear forces which occur in production. The sand particles can penetrate, for example, into the production chain, into pumping apparatus underground and at the surface, and into installed water separators and pipeline systems, and lead therein to corrosion, abrasion, or to faults and reduced function.
It is also known that production boreholes can be stimulated by breaking up hydrocarbon-containing rock (known as fracturing). In order to keep the cracks obtained open over a prolonged period even under production conditions, proppants, for example sands or bauxite particles, are pumped into the cracks obtained. Such particles can likewise be discharged from the fissure as described. In addition to the problems described above, this can additionally lead to the effect that the cracks formed in the rock close again and the production rate of the hydrocarbon produced declines significantly.
The prior art discloses various techniques for preventing the discharge of sand from the formation together with the hydrocarbon-water mixture into the borehole, the subsequent production chain and the equipment used.
For example, gravel packings and mechanical sand filters can be installed in the production borehole in order to suppress the transport of sand out of the borehole. Such systems are described, for example, in CA 2,314,392 or US 2008 217 002 A1.
Secondly, a mobile resin can be pumped into the unconsolidated sand layer and cured therein. In the systems described in the prior art, according to the temperature in the borehole, an appropriate hardener, for example an organic amine, can be added. The resin can be pumped into the formation together with the hardener directly as a liquid or applied to a carrier, for example small sand particles. The resin causes contact adhesion of the sand grains present in the formation, such that the sand grains can no longer be discharged, but it is still possible for the hydrocarbon to flow through the now consolidated sand.
The cured resin has to be stable to hydrolysis over a long period in the borehole at the deposit temperatures which exist, and must also not be dissolved at all by the hydrocarbon produced.
For example, GB 1,172,116 and GB 1,453,001 describe the use of furfuryl alcohol-based resin systems which are pumped into the formation in an organic solvent. DE 28 43 452 and CA 2 637 696 describe systems based on epoxy resins.
In other fields of industry too, there is a need to consolidate inorganic particles by means of suitable measures, for example in mining, in order to prevent the detachment of loose rock when tunneling, or else protect rock from weathering or oxidation. For example, CA 2 497 722 describes the use of two-component elastomeric resin systems which are applied to the surface of the rock and lead to film formation there.
Further examples comprise the prevention of dust evolution or the consolidation of soil. For instance, RU 2151301 describes the prevention of dust evolution by binding the dust with polyvinyl butyral and sand.
The consolidation of sand in above-ground applications is likewise of great industrial interest. For example, molds are produced for a wide variety of different applications, for example for metal casting, from sand with the aid of adhesives. For instance, applications CN 1075114 A, DE 24 00 908, DE 1012035 and JP 02 197 348 A2 describe the use of urea-formaldehyde resins for production of molds, using different molar ratios of urea to formaldehyde and different hardeners.
It is also known that the use properties of such molds can be improved by adding further additives, for example furfuryl alcohol (DE 1160141), the conversion of urea-formaldehyde resins to sulfonates (Yang, Ming et al. Beijing Huagong Daxue Xuebao, Ziran Kexueban (2003), 30(4), 81-84) or the addition of phenol-containing additives (CS 247931).
The consolidation of sand layers, both above and below ground, by means of urea-formaldehyde systems is disclosed by US 2006 240995, U.S. Pat. No. 6,311,773, RU 2048950 and U.S. Pat. No. 5,670,567.